1. Field of the Invention
This invention relates to a key switch device and, particularly, to a key switch device of the link type used for a thin keyboard of a notebook-type personal computer.
2. Prior Art
A conventional key switch device of this type will be described with reference to FIGS. 6 to 8. In FIG. 6(a), reference numeral 1 denotes a key switch device that is schematically diagramed. The key switch device 1 is of the so-called pantograph link-type in which two link members 4 and 5 are crossing in an X-shape between a base plate 2 and a key top 3, the key top 3 being supported by a rubber spring (not shown) interposed between the base plate 2 and the key top 3, and by the link members 4 and 5. Referring to FIG. 6(b), the link members 4 and 5 have a nearly U-shape, and are fitted together at fitting portions 6 and 7 so as to freely turn. The link member 4 is rotatably supported by shafts at rotary portions 4a and 4b at its upper both ends thereof by bearing portions 3a and 3b provided at the lower ends of the key top 3, and slidably engages at slide portions 4c and 4d at lower both ends thereof with slide guides 2a and 2b formed in the base plate 2. The other link member 5 slidably engages at slide portions 5a and 5b at upper both ends thereof with slide guides 3c and 3d formed in the lower ends of the key top 3, and is rotatably supported by shafts at rotary portions 5c and 5d at lower both ends thereof by bearing portions 2c and 2d provided on the substrate 2. The bearings 3a, 3b, 2c and 2d are the ones with a slit.
When depressed, the key top 3 is lowered maintaining nearly a horizontal state due to the linking action of the link members 4 and 5, whereby a switching member (not shown) provided on the base plate 2 is depressed to render the switching member conductive.
FIG. 7(a) is a diagram illustrating the direction of operation of the key switch device 1. The key top 3 of the key switch device 1 is depressed at a depress angle of about 90 degrees with respect to the surface of the base plate 2.
FIG. 7(b) illustrates a state where the key switch device 1 is mounted on a keyboard 8 that is installed being inclined at an angle xcex1 with respect to the horizontal plane. When depressed by a finger 9 of a person who operates the keyboard, the key top 3 of the key switch device 1 is lowered at an angle xcex1 of inclination that is added to the depress angle of nearly 90 degrees with respect to the horizontal plane. Here, the angle xcex1 of inclination is, in practice, a limited angle. Therefore, the direction of depress by the finger 9 of the person operating the keyboard and the direction of depress of the key top 3, differ greatly toward the upper side of the keyboard 8 to deteriorate the feeling of operation.
FIG. 8 illustrates a curved keyboard 10 for a desktop use, which is generally regarded to offer the most desirable operability. In the curved keyboard 10, the upper surfaces of the key tops 3 are arranged being so curved that the angle of inclination increases from the lower side toward the upper side to meet the motion of the finger 9.
The above arrangement of the curved keyboard 10 may be desirable. When the above arrangement cannot be realized, however, the depress directions of the key tops 3 of the key switch device 1 may be so improved as to approach those of the above curved keyboard 10, in order to improve the operation feeling of the key switch device 1.
In the above-mentioned conventional key switch device, the two link members are crossing in an X-shape between the base plate and the key top constituting the so-called pantograph link system, and the key top is supported by the rubber spring and by the two link members.
Therefore, the two link members have fitting portions that fit together in a crossing manner and further have two rotary portions and two slide portions, respectively. That is, the switch device has a total of 10 moving support portions. However, the moving support portions have a small strength. In particular, the portions where the link members are fitted together have a small strength, hindering the effort for realizing the key switch device in a reduced thickness.
Further, the slide portions of the key top of the key switch device are injection-molded using a metal mold of a complex shape, the metal mold being manufactured requiring an increased cost.
Besides, the key top is supported at four points at the lower ends thereof by using the link members, two points among the four points being supported by slide portions. Accordingly, the surface of the key top tends to be tilted to develop play; i.e., the surface of the key top is not maintained in a horizontal state.
Moreover, the key top is depressed at an angle of nearly 90 degrees with respect to the surface of the base plate, which is greatly different from the direction of depress by a finger of the operator, deteriorating the operation feeling. Thus, there arouses a technical problem that must be solved for realizing a key switch device that features an increased strength, a decreased thickness yet being produced at a decreased cost and offering a favorable operation feeling. The object of this invention is to solve this problem.
This invention was proposed in order to achieve the above object, and provides a key switch device in which a key top is mounted on a base plate via a rubber spring so as to be freely lifted and lowered, and the switching operation is effected upon depressing the key top, wherein a small link member and a large link member are provided between the base plate and the key top so as to turn at right angles without contacting to each other, the lower ends of the small link member are slidably fitted into slide guides formed in the base plate, the upper ends thereof are supported by bearing portions with slit provided at the lower ends of the key top, the lower ends and the upper ends of the large link member are supported by the bearing portions with slit provided on the base plate and at the lower ends of the key top, and the key top is supported by the rubber spring, by the small link member and by the large link member so as to be freely lifted and lowered.